Beethoven's Anvil takes us inside modern and ancient performances and rituals to show how the musical linking of brains explains things we commonly (and not-so-commonly) experience. Benzon shows us a rehearsal where mysterious tones that no one is playing seem to emerge from the ceiling, but only when the musicians feel they are in a groove. Everyone present hears these tones - but are they an acoustic phenomenon or a mental one? He explores how Leonard Bernstein knew he'd given a good performance when, after it was over, he felt he hadn't just performed a piece but written it; and how performers as different as Earl "Fatha" Hines and Vladimir Horowitz felt they stopped being human onstage but became something like racehorses. Benzon uses remarkable insights from brain science and anthropology to investigate musical styles ranging from Gregorian chant to hip-hop; discovers a children's song in a Louis Armstrong solo and finds that it may date to before the Crusades; explains rock music's merging of African and European musical forms in evolutionary terms; and reveals the similarity between decision-making in a baboon troop and the final movement of Beethoven's Ninth Symphony.